Lignite Deposition and Marine Cycles the Austrian Tertiary Lignite
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Lignite©Akademie d.deposition Wissenschaften Wien; download and unter marine www.biologiezentrum.at cycles The Austrian Tertiary lignite deposits - A case history By FRITZ F. STEININGER, Institut für Paläontologie der Universität Wien, A-1010 Wien, Universitätsstr. 7/II, Austria FRED KÖGL, Naturhistorisches Museum Wien, Burgring 7, A-1014 Wien, Austria PETER HOCHULI, ESSO EPR-E, 213 Cours Victor Hugo, F-33321, Begles, France CARLA M ü l l e r , 1 Rue Martignon, F-92500 Rueil-Malmaison, France (Vorgelegt in der Sitzung der mathem.-naturw. Klasse am 13. O ktober 1988 durch das w. M. Walther E. Petrascheck) C ontents: Zusammenfassung Abstract Introduction Lignite accumulation, marine cycles, paleogeography and climate Lignitophile phases in the Austrian Tertiary: Gosau cycle (Early Eocene) Molasse Cycle (Late Eocene to Early Miocene) Intramountain-basin cycle (Middle Miocene to Late Miocene) Conclusions References Zusammenfassung: Am Beispiel der tertiären Kohleablagerungen in Österreich werden die Zusammenhänge zwischen Kohlebildung und marinen Trans- und Regressionszyklen aufgezeigt. Ferner können mit Hilfe palynologischer Studien direkte Beziehungen zwischen Kohlebildungsphasen und Klima entwicklung aufgezeigt werden. Im Känozoikum Österreichs werden drei tektonisch begründete Sedimentationszyklen mit Kohleführung unterschieden: Gosau Zyklus (Unter-Eozän) Molasse Zyklus (Ober-Eozän bis Unter-Miozän) Intramontaner Beckenzyklus (Mittel- bis Unter-Miozän) Kohlebildungsphasen finden sich: im Untereozän der zentralalpinen Gosau Formation; im Obereozän des Untergrundes der Molassezone; im Mitteloligozän und im Untermiozän in nördlichen Buchten und im Oberoligozän am Westrand der Molassezone. In den intramontanen Becken fallen die bedeutendsten Kohlebildungsphasen in das Karpatien und das Mittel- bis Obermiozän. Die mittel- und obermiozänen 310 F r itz F. St e in in g e r et al., Kohlelagerstätten©Akademie der d. Molassezone Wissenschaften Wien; wurdendownload unter unter www.biologiezentrum.at denselben Bedingungen wie jene in den intramontanen Becken gebildet. Möglichkeiten für eine ökonomische Kohleexploration in Österreich sind nur im Paläogen des Untergrundes am Nordrand des Molassebek- kens gegeben. Die im österreichischen Känozoikum bekannten Kohlebildungspha sen stehen im unmittelbaren Zusammenhang mit den weltweit auftreten den marinen (transgressiven) Zyklen und korrelieren in diesem Sinn mit den meisten übrigen tertiären Kohlelagerstätten in Europa. Diese Fallstudie zu den Kohlebildungsphasen in Österreich könnte als Basis einer erfolgreichen Untergrund-Kohleexploration dienen. A bstract The close relation between coal-accumulation and marine transgres- sive cycles is demonstrated by the Austrian Tertiary lignite deposits. Furthermore, palynological investigations show a direct correlation to climatic conditions. Three tectonically caused sedimentary cycles with lignite deposition are distinguished: Gosau cycle (Early Eocene) Molasse cycle (Late Eocene to early Miocene) Intramountain-basin cycle (Middle Miocene to Late Miocene) Within these cycles important phases of lignite deposition are: the Early Eocene of the Central Alpine Gosau formation; the Late Eocene in the subsurface of the Molasse-Zone; the Middle Oligocene and Early Miocene in the northern bays and Late Oligocene on the western edge of the Molasse-basin. In the intramountain-basins, the main lignite phases are located in the Early/Middle-Miocene and Late Miocene. The Middle- and Late Miocene lignites of the Molasse-Zone are formed under the same conditions as the lignites in the intramountain-basins. Possibilities for economic lignite exploration in Austria are given only in Paleogene deposits of the subsurface of the northern areas of the Molasse-basin. The lignite phases known from Austrian Tertiary deposits are related directly to worldwide marine (transgressive) cycles and can be seen in connection with most of the other European Tertiary lignite deposits. The methodology demonstrated that the Austrian case history could serve as a basic assumption for a successful subsurface coal exploration. Introduction The oil crises and concern about future energy resources have caused a renewed worldwide interest in coal as a main energy source. The Tertiary lignite deposits are of main interest in this connection, especially in the northern hemisphere where large reserves are known at present. Up until now, coal exploration in the Austrian Tertiary has been carried out only on coal indications cropping out on the surface and by extending Lignite deposition and marine cycles 311 previously known©Akademie deposits. d. Wissenschaften Lignite Wien; download indications unter www.biologiezentrum.at as well as smaller and larger coal seams and measures are widespread in the Tertiary of the intramountain basins and the Molasse-Zone. These deposits have been quarried since the middle of the 18th century; most of the mines, especially those in inneralpine areas, are now closed down. Overviews and monographic papers concerning Austrian coal deposits and mines have been published by: KOMITEE ALLGEM. B ergmannstag (1903), P e t r a s c h e c k (1922-1929; 1937), W e b e r & W eiss (1983) and Z a p f e (1956). Lignite-exploration research has been supported during the past several years by the Ministry for Economical Affairs, the Geological Survey, the States of Austria, the Academy of Sciences, the Austrian Science Foundation and the Austrian Coal-Mining Companies (see FETTWEIS, 1982; THIELE, 1983). The goal of this study is to test the hypothesis of coal measure formation in the Austrian Tertiary deposits in relation to marine trans- and regressive cycles. This would provide a new prospective of lignite exploration, especially for subsurface coal deposits. Most lignite deposits were formed in the transition between marine and continental facies belts. Successful exploration, however, must initially take all geological features related to basin development into account. In addition to a tectonical analysis, stratigraphy, paleogeogra- phic reconstruction, paleoclimatology and facies analyses are important. Geophysical investigations and deepdrilling should commence only after these analyses and the relevant geological surface studies have provided a prognosis on lignitophile phases and possible lignite exploration areas. These procedures were recommended by LÜTTIG (1971, 1977) and POHL (1981) for successful and economic exploration strategies. This study was undertaken at the suggestion of Prof. Dr. W. E. PETRASCHECK, to whom we are very grateful for his support. The Austrian Academy of Sciences, commission on „Grundlagen der Mineral- Rohstoff-Forschung“ supported this investigation financially under Project Nr. 4223. Lignite accumulation, marine cycles, paleogeography and climate In contrast to the methods normally used (expensive drilling operations, etc.) to survey the geological situation of sedimentary basis with possible coal measures the encouragement of LÜTTIG (1971, 1977) proposed the following scientific approach: First of all the possibilities of coal measure deposition in a given sedimentation area as well as the possible sequence of lignitophile phases should be clarified. The accumulation of lignites is apparently directly related to marine transgressive and regressive phases and tectonics. ÄHRENS & al. (1968) already demonstrated a clear relation between the generation of the lignite deposits in northern Germany and the upper Oligocene and lower Miocene marine transgression in this area. In the coal measures of the Lausitz, paralic coal seams are dominant in regressive 312 F r itz F. St e in in g e r et al., cycles („Schuttfächerrandflöz“);©Akademie d. Wissenschaften Wien; these download seams unter www.biologiezentrum.at are clearly distinguished from the epirogenic seam type. Studies of recent peat accumulations in the Mississippi Delta (KOSTERS & al., 1987) showed the largest quantities of organic, low ash material accumulations in cut off freshwater basins of the delta; during transgressive events, accretion of organic material (up to 35 %) took place in saltwater marshes. The significance of large scale tectonic movements in relation to the formation of intramountain basins and lignite deposition was demonstra ted by CECH (1980) for the western Carpathian mountains. NEBERT (1983 a), in his detailed studies of sedimentary sequences of intramoun- tain-basins, clearly pointed out that lignite accretion constitutes a member of the sedimentary cycle. The cycle starts with a fluviatile phase with coarse material. The raising of the groundwater table transforms the fluviatile cycle into a limno-fluviatile phase with sand and clay sedimentation. This phase is followed by a telematic (peat-forming) phase of lignite accretion and is terminated by limnic sedimentation of marls or limestones. The following fluviatile sediments fill up the basin. A fundamental summary of requirements for lignite formation was given by LÜTTIG (1968, 1971, 1977): initially humid, peat-forming climatic conditions must cause intense growth of peat or lignite- generating plant associations. For this process he postulates a rising groundwater table, a condition which in general is caused in connection with marine transgressive settings. Furthermore, synchronous tectonic movements must provide the necessary space in the form of sedimentary traps or basins. During this process, basin subsidence, the sedimentation rate and peat accretion, as well as the rise of the groundwater table